Electric igniter



L. A. LINDBLAD 3,056,350

ELECTRIC IGNITER Filed Aug. 20, 1959 Oct. 2, 1962 FIG. I FIG. 2

IN VEN TOR.

LA RS ALFRED L/NDBLAD BY HQMM A -r TORNEYS United. States Patent 3,056,350 ELECTREC IGNITER Lars Alfred Lindblad, Utiriksbacken 23, Grondal, Sweden Filed Aug. 20, 1959, Ser. No. 835,10tl Claims priority, application Sweden Oct. 11, 1954 3 Claims. (Cl. 102-28) The present invention relates to electric igniters or primers as used in connection with fuses for detonating an explosive and especially with fuses for ammunition.

Igniters of the general kind above referred to, generally comprise two conductors such as wire conductors of adequate current carrying capacity, the ends of which are physically separated, but are electrically joined by a thin conductive layer generally produced by plating and coated with an ignitable explosive. The heating of this coating when an appropriate current is applied to the wire conductors, produces the desired ignition or priming action.

As is apparent, the adjacent ends of the wire conductors must on one hand be separated from each other and on the other hand they should be as close to each other as possible so that a minimum energy is required to heat the conductive bridge between the twowire ends to the ignition temperature.

It has been found difficult in practice to reconcile the aforementioned two conditions, the more so as igniters as here involved are and must be an inexpensive mass production item.

It is an object of the present invention to provide a novel and improved igniter of the general kind referred to, the wire conductor ends of which can be safely placed closer to each other than was heretofore possible so that igniters according to the invention can be activated by employing a minimum energy.

Another object of the invention is to provide a novel and improved igniter, the structural design of which lends itself to placing the conductor wires and more specifically the ends thereof very close to each other by simple and inexpensive production methods without a risk of causing electric contact between the conductor wires at points other than the ends bridged by the conductive layer.

Still another object of the invention is to provide a novel and improved electric igniter in which the wire ends are bridged by a conductive layer which can be produced by a very simple and efficient manner without requiring the use of high temperatures or plating operations involving the use of a bath aggressive to insulation material.

Other and further objects, features and advantages of the invention will be pointed out hereinafter and set forth in the appended claims forming part of the application.

Certain features of the present invention are disclosed but not claimed in my co-pending application Serial No. 535,944 filed September 2, 1955 now Patent 2,907,100.

The present application is a continuationsin-part of my co-pending application Serial No. 535,949 filed September 22, 195 5, now abandoned.

In the accompanying drawing, several preferred embodiments of the invention are shown by way of illustration and not by way of limitation.

In the drawing:

FIG. 1 is a perspective side view of an electric igniter or primer according to the invention.

FIG. 2 is a similar view of a modification of the ignitcr, and

FIG. 3 is a plan view of the igniter according to FIG. 2 an an enlarged scale.

Referring now to the figures in detail, FIG. 1 shows an igniter comprising two electric wire conductors 1 and 2. Conductor 1 is covered with insulation material and conductor 2 is left bare. Any suitable insulation material Patented Oct. 2, 1962 may be used, but an insulating lacquer coating is generally preferable. The two conductors are closely held together at juxtaposed ends, and this is effected by twisting the respective end portions 4 and 5. As is apparent, the twisted wire portions can be brought so closely to each other that the spacing between the wire parts 4 and 5 does not appreciably exceed the thickness of the insulating coating on conductor 1. The twisted conductor ends are embedded in an insulation body 6 which has preferably about a semi-spherical shape. Body 6 is advantageously formed of a hardening insulation material of a kind such that the embedding of the twisted con ductor ends does not require a temperature high enough to damage the insulating coating on conductor ll. There are known many insulating materials suitable for the purpose, such as hardening synthetic resins. The end faces of the two conductor portions 4 and 5 are bare and substantially flush with the plane surface of body 6.

Body 6 may have a variety of suitable shapes other than the illustrated semi-spherical shape provided only that the conductor ends 4 and 5 are laid bare flush in an outer surface of the body.

The igniter according to FIG. 2 differs from the igniter just described only in that both conductors 1 and 2' including the twisted end portions 4' and 5' are covered with insulation coatings 7 and 8 respectively. As is apparent, the minimum distance between the two wire ends laid bare in the plane surface of body 6 is twice the thickness of the insulation coating whereas in the embodiment of FIG. 1 it needs to be only once the thickness of the coating. But even twice the thickness of the coating is still much closer than was heretofore possible, and the use of insulation coating on each of the conductors affords an additional safety factor against a direct short circuit between the two conductors.

My aforementioned two co-pending patent applications describe in detail a suitable method of producing igniters according to FIGS. 1 and 2. The arrangement of the conductive coating electrically bridging the exposed and embedded wire ends can best be apprehended from FIG. 3. This figure shows an enlarged plan view of FIG. 2, that is the bare ends of wires 4' and 5' covered with insulation coating 7 and 8 respectively are flush with the plane surface of body 6. A coating 9 covers all or part of the plane surface of body 6 and in any event at least the surface area including wire ends 4 and 5'. The coating comprises a suitable binder such as a hardening adhesive liquid into which are mixed discrete particles 9 of an electrically conductive and magnetizable material such as iron particles. The particles are oriented to form a multitude of continuous coherent pathways which bridge the two conductor ends as is indicated in FIG. 3. The orientation of the particles can be readily effected by subjecting the same to a magnetic field prior to the hardening of the coating liquid. Suitable arrangements for magnetizing the coating material are fully described in my aforesaid co-pending applications.

As is evident, the orientation of magnetizable particles by a magnetic field affords the advantage of a minimum of conductive material for forming a conductive bridge between the two conductor ends. Accordingly, a minimum of energy is required to heat the coating when the igniter is activated to set off an explosive charge. Clearly any solid conductive layer such as heretofore used, must contain considerably more metal however thin it may be than the pathways formed by the oriented particles. Accordingly, the current required to activate the igniter is correspondingly higher.

In order to ready the igniter for actual use, the plane surface after having been coated with the conductive material is further coated with a suitable ignitable explosive such as acetylene silver.

Experience and tests have shown that finished igniters according to the invention can be mass-produced so uniformly that existing differences, if any, are negligible.

While the invention has been described in detail with respect to certain now preferred examples and embodiments of the invention it will be understood by those skilled in the art after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. An electric igniter for use with a fuse for an explosive, said igniter comprising two conductors, a body of solid insulation material, one end of each of said conductors being embedded in said body, the two embedded ends terminating flush with a surface of the body close to but electrically insulated from each other, and a coating covering the surface portion including said two conductor ends, said coating including electrically conductive and magnetizable discrete particles, magnetically oriented into direct contact one with another in the form of metallically coherent pathways within said coating, said pathways constituting a conductive bridge between said two exposed conductor ends.

2. An electric igniter for use with a fuse for an explosive, said igniter comprising two wire conductors, at least one of said wires being covered with insulation material, said wires being secured to each other in close juxtaposition at one end and extending into the same general direction from the juxtaposed end portions, a body of solid insulation material, said juxtaposed wire portions being embedded in said insulation body terminating flush with :a surface thereof, and a hardened coating covering the surface portion including said exposed wire ends and comprising a binder and discrete electrically conductive and magnetizable particles magnetically oniented into direct contact one with another in the form of metallically coherent pathways within the coating, said pathways constituting a conductive bridge within said two exposed wire ends.

3. An electrical igniter according to claim 2 wherein the portion of the insulation body covered with said coating is a plane surface portion.

References Cited in the file of this patent UNITED STATES PATENTS 2,708,877 Smits May 24, 1955 2,754,757 MacLeod July 17, 1956 2,762,302 MacLeod Sept. 11, 1956 2,924,140 Scherrer Feb. 9, 1960 2,942,546 Liebhafsky et al. June 28, 1960 

